In order to provide a more compact format for identifying mixtures of refrigerants in the following discussions, mixtures of refrigerants will be listed in the form of:R-ABC/DEF/GHI N0/N1/N2which represents a mixture of refrigerants (fluids) R-ASC, R-DEF, and R-GHI where N0, N1, and N2 are the weight percentages of each component refrigerant fluid, and N0+N1+N2=100; or in the form of:R-ABC/DEF/GHI N0−N0′/N1−N1′/N2−N2′which is similar, but specifies ranges of the weight percentages each of the component refrigerant fluids, with the total of the weight percentages being 100 percent.
Zeotropic (nonazeotropic) mixtures of refrigerants will change composition if they are allowed to leak as vapor phase from a container containing all components of the refrigerant mixture in both vapor and liquid phases. Single component and azeotropic mixtures of refrigerants do not change composition appreciably from vapor leakage. Single component and azeotropic mixtures of refrigerants have only one boiling point temperature for a given pressure, provided the refrigerant exists as both liquid and vapor states in the container. Zeotropic mixtures of refrigerants will boil over a range of temperatures at a given pressure. As the temperature is raised, the point at which the first bubbles appear (constant pressure) in the liquid is known as the “bubble point,” which is roughly analogous to the boiling point of a single component or an azeotropic mixture. Starting in a vapor phase and lowering the temperature (at a constant pressure) to the point where the first droplet of liquid forms defines what is known as the “dew point” of the mixture of refrigerants. The difference between the bubble point temperature and the dew point temperature is known as the temperature “glide”. A pressure gauge connected to a cylinder containing a zeotropic mixture of refrigerants will read the bubble point pressure for the corresponding temperature of the refrigerant mixture.
Under the Montreal Protocol, as amended, United States laws (1990 Clean Air Act), and U.S. Environmental Protection Agency rules, the production and importing of R-12 ended on Dec. 31, 1995. Additionally, only 15% of the baseline amounts of chlorinated fluorocarbons (CFCs) was allowed to be produced or imported into the U.S. during the year 1995 adjusted on an ozone depletion factor basis. R-12 is the major share of that production.
With the effective date of the ban on U.S. R-12 production and importing having passed (Dec. 31, 1995), one industry option has been to retrofit R-12 refrigeration or air conditioning systems, both stationary and automotive, to R-134a (tetrafluoroethane). The mineral oils used in R-12 systems are completely immiscible in R-134a, however, as the industry has therefore developed new oils, which are either polyalkylene glycol (PAG) based (for automotive) or polyol ester (POE) based (stationary refrigeration and some automotive retrofit).
While PAG oils are good lubricants, and are miscible in R-134a at typical evaporator temperatures, they have two main problems. First, most PAG oils cannot tolerate even minute traces of residual chlorides that remain in the R-12 refrigeration or air conditioning systems that have been purged of R-12. These chlorides are dissolved in the small amount of mineral oils which cannot be flushed out or are in coatings on the inside of aluminum piping (aluminum chloride from previous R-12) or are dissolved in rubber hoses. The presence of chlondes greatly accelerates the breakdown of most PAG oils.
It has been reported in the literature that test systems that were flushed with R-11 (trichlorofluoromethane) and then retrofitted to PAG oil and R-134a, sustained catastrophic compressor failures within one week due to oil breakdown. R-11 has a greater affect on PAG oil breakdown than does R-12. It was common practice in the automotive air conditioning service industry, into the early 1990s, to flush R-12 systems with R-11 to remove contaminates. The traces of R-11 remaining do not interfere with R-12 operation, but could cause premature failures if R-12 systems are ever retrofitted to R-134a and PAG oils.
The second main problem with PAG oils is that PAG oils are in the order of 100 times more hydroscopic (absorb moisture) than are R-12 mineral oils. During assembly, service, or after an accident, automotive R-134a systems may be exposed to atmospheric moisture which will be absorbed into the PAG oil. Extreme care is therefore required during servicing of PAG oil systems to prevent exposure to atmospheric moisture, especially in humid climates.
The stationary refrigeration industry has overwhelmingly chosen POE-based oils for R-134a systems, for both new systems and those retrofitted from R-12. POE oils can tolerate residual chlondes much better than PAG oils, however POE oils have problems also. POE oils are on the order of 10 times more hydroscopic than are R-12 mineral oils POE oils, in general, do not have as good lubrcities as do the PAG and mineral oils. Steel is a known catalyst that facilitates the breakdown of most POE oils at the higher temperatures encountered in refrigeration systems. The industry has had to develop passivators and additive packages for POE oils to try to counter this problem. Moisture and other contaminates may cause the POE oils to break down into their constituent fatty acids and alcohols.
Many industry R-134a retrofit procedures for R-12 stationary refrigeration and air conditioning systems call for 3 to 5 changes of the compressor oil (to a POE) in order to reduce the residual mineral oil to below about 1 percent to about 5 percent by volume. Most small to medium sized (up to 10 tons in capacity) hermetic compressors in R-12 equipment do not have oil drains. Therefore, the compressor must often be removed and the oil dumped out up to 5 times for a retrofit to R-134a. This entails unbrazing the low and high side refrigeration pipes from the compressor and rebrazing them up to 5 times. The brazing temperature is about 1100 degrees Fahrenheit. Service technicians often do not go to the trouble to bleed a relatively inert gas such as dry nitrogen or CO2 through the piping during brazing operations. Brazing temperatures cause the copper piping to oxidize on the inside forming “scale” which flakes off and adds to the contamination of the system. The oil coating the inside of the piping breaks down and carbonizes, adding more contaminates. Even worse, refrigerant vapors are present in the pipes during brazing, they decompose into hydrochloric and hydrofluoric acids, which greatly add to system contamination and premature failure. Finally, the physical operation of removing the compressor 5 times, and inverting it to remove oil, can allow metal flakes and other sludge which have accumulated in the bottom of the compressor oil sump to break loose and end up on the top of the inside of the compressor shell. Upon reinstalling the compressor this sludge and metal flakes may drop onto the top of the compressor and get into motor windings (causing shorts and motor burnouts, or get into the intake valves and cause mechanical problems (seized compressor).
There have been several reports that both POE and PAG oils causing skin rashes or burns to service technicians This has necessitated additional safety procedures, such as wearing gloves, were handling these oils. Unless a hermetic compressor motor burnout has occurred, R-12 mineral oils have not caused skin rashes and burns to service technicians. A hermetic compressor motor burnout causes some of the refrigerant to decompose into hydrofluoric and hydrochloric (if the refrigerant contains chlorine atoms) acids, and may cause skin bums no matter what oil is used
Some compressors built for R-12 and retrofitted to R-134a with POE oils have been reported by compressor manufacturers to fail from lubrication problems caused by the lack of the “foaming” of the POE oils in the compressor crankcase, Some compressor designs relied on the fact that mineral oils and R-12 generated foaming in the compressor crankcase in order for the oil to reach and lubricate certain parts of the compressor. New compressors designed for R-134a and POE oils use other means to make sure all the parts are property lubricated.
Compressors manufactured for R-12 and mineral oil use often were constructed with a paraffin based wax coating on the motor windings as an aid to building the motor without breaking the wire during the motor winding phase of the construction. When retrofitted to R-134a and POE oils, the paraffin would sometimes come off the windings, and not dissolve in the R-134a refrigerant and POE oils, and circulate through the system as solids and plug up the refrigerant metering device, usually a capillary tube, causing the system to fail. R-12 (or a substitute with adequate mineral oil miscibility) and mineral oil, just dissolve the pieces of paraffin wax which come off the motor windings and therefore do not clog the refrigerant metering device.
Finally, the low critical temperature of R-134a (213.9 degrees Fahrenheit) verses the critical temperature of R-12 (233.2 degrees Fahrenheit) can cause abnormally high head pressures in hot ambient conditions in systems designed for R-12. For automotive applications, stopped traffic or hot climates can cause a reduction in R-134a performance. Systems designed for R-134a often increase the size of the condenser about 50 percent over tie size similarly designed R-12 system condenser. Stationary systems, such as vending machines, now retrofitted to R-134a may see high head pressure and low performance problems when the condenser becomes slightly fouled by dirt and dust R-12 systems can run much longer between cleanings to remove dust and dirt from the condenser than similar systems converted to R-134a.
R-406A is a known ternary mixture of refrigerants, consisting of isobutane (R-600a), chlorodifluoroethane (R-142b), and chlorordifluoromethane (R-22) that provides a “drop-in” substitute for dichlorodifluoromethane (R-12) refrigerant. R-406 is described in U.S. Pat. Nos. 5,151,207 and 5,214,929, the disclosures of which are incorporated herein by reference.
In addition to being a suitable “drop-in” substitute for R-12, R-406A has been successfully used as a “drop-in” substitute for refrigerant R-500 (azeotropic mixture of R-12 and R-152a with weight percentages of 73.8 and 26.2. respectively) in many instances. R-152a is 1,1-difluoroethane.
Refrigeration systems with refrigerant metering devices consisting of a capillary tube or a fixed orifice have had excellent results with R406A as a “drop-in” substitute. Some R-500 systems with “thermostatic expansion valves” (TEVs), have needed the “power head” of the expansion valve changed to an R-12 head, while others have performed satisfactory.
Several other attempts have been made to create the ideal “drop-in” substitute for R-12. Some do not return mineral oil to the compressor property at temperatures of desired operation (i e Forane® FX-56 (R-124/142b/22 25/15/10) also known as R-409A, U.S. Pat. No 5,188,749; and FRIGC™ FR-12™ (R-600/124/134a 2/39/59), U.S. Pat. No 5,425,890) Changing the compressor oil from mineral oil to alkylbenzene oil will often correct the oil return problems, but now an oil change is necessary and the refrigerant is no longer a “drop-in” substitute for R-12.
Some attempts have provided temperature-pressure curves which are not always suitable for operation of R-12 equipment. The Forane® FX-56 refrigerant temperature-pressure curve is too high, which results in excessive head pressures, refrigerant breakdown and compressor failures in many instances. See FIG. 1 for the Foran® FX-56 temperature-pressure chart FRIGC™ FR-12™, on the other hand, has a temperature-pressure curve which is too low, which results in low system capacities, and causes problems if system low pressure cut out controls are not replaced or adjusted. See FIG. 1 for the FRIGC™ FR-12™ temperature-pressure chart. FRIGC™ FR-12™ used in an automotive air conditioning system should produce suction side pressures of about 18 to about 23 gauge pressure (PSIG), whereas R-12 would produce about 28 to about 32 PSIG. This causes the low pressure controls to prematurely open, falsely sensing low-charge or too cold conditions. Once opened, the compressor clutch disengages, stopping the compressor, and the system equalizes in pressure, and restarts. This results in poor capacities, and excessive clutch wear from cycling every few seconds. Automotive variable displacement compressors, such as the GM V-5, try to maintain a constant suction pressure, usually about 28 to about 30 PSIG for capacity control. The lower than R-12 temperature-pressure curve of FRIGC™ FR-12™ fools these compressors into operating at a much lower displacement than for R-12 under given load conditions, thus greatly reducing capacities (in the order of 50 percent reduction or more). If a large amount of FRIGC™ FR-12™ (3 pounds or more), is allowed to vapor leak under ambient temperatures of about 10 degrees to about 25 degrees Fahrenheit. The remaining mixture may possibly first go weakly flammable then highly flammable near the very end of the leak out (90 weight percent or more of the mass has leaked). The boiling point of their highest boiling point component. R-600 (n-butane), is 31.03 degrees Fahrenheit, while their next lower boiling point component is R-124, with a boiling point of 8.26 degrees Fahrenheit.
These foregoing and additional known refrigerant mixtures are summarized below. Some are disclosed in research papers and others in U.S. Patents, while still others are commercial products on the market.    R-124/22 60/40    Has poor mineral oil miscibility. See U.S. Pat. No. 4,303,536.    R-124/125 65/35    Almost nonexistant mineral oil miscibility, and the glide is too high    R-124/142b/22 25/15/60    This is Elf Atochem Forane® FX-56, or R-409A. See U.S. Pat. No. 5,188,749. Forane® FX-56 has poor mineral oil miscibility, and the temperature-pressure curve is too high. It is sometimes claimed to be an R-12 “drop-in”, other times claimed to be near “drop-in” requiring changing oil to alkylbenzene type to assure miscibility. Six hours of operation in the oil miscibility test stand described in Appendix A, caused moderate oil logging in the evaporator and suction line at an evaporator temperature of about 10 degrees Fahrenheit using Suniso 3GS (150 viscosity) mineral oil, standard for systems of this type. Severe oil logging occurred around −20 degrees Fahrenheit, with two phase (oil and liquid refrigerant) and “milky” solutions observed in the evaporator. Pure R-22 performed much the same way. The “milky” solution is caused by an immiscible “dispersion” of oil and liquid refrigerant. After severe oil logging from Forane® FX-56 at about −20 degrees Fahrenheit, the Forane® FX-56 was removed, and the oil miscibility test stand was charged with the refrigerant mixture later described in Example 1. Two hours of operation with Example 1 returned almost all the oil to the compressor, operating at about −30 degrees Fahrenheit.    R-22/124/142b 65/25/10    This is Elf Atochem Forane® FX-57, or R409B. This mixture will have even less miscibility in mineral oil than Forane® FX-56. Forane® FX-57 will also have an even higher temperature-pressure curve than Forane® FX-56 due to more R-22 component and less R-142b component.    R-124/152a/22 24/13/53    This is DuPont SUVA® MP-39, or R-401A. See U.S. Pat. No.4,810,403. R-401A has poor miscibility in mineral oils. DuPont recommends at least 80 volume percent of the compressor oil be changed to alkylbenzene type to assure miscibility R-401 A works fine provided compressor oil is changed.    R-124/152a/22 61/11/28    This is DuPont SUVA® MP-66, or R-401 B. The same comments for R-401A apply here as well.    R-124/152a/22 33/15/32    This is DuPont SUVA® MP-52, or R-401C. The same comments for R-401A apply here as well    R-600/124/134a 2/39/59    This is Intermagnetics General Corporation (IGC) FRIGC™ FR-12™. See U.S. Pat. No. 5,425,890 FRIGC™ FR-12™ claims to be a “drop-in” for R-12, but the temperature-pressure curve is about 8 degrees Fahrenheit too low at evaporator temperatures (32 degrees Fahrenheit) in automotive air conditioning systems, causing low capacity, excessive compressor cycling and rapidly wearing out compressor clutches. Excessive clutch cycling may be eliminated by replacing low pressure cutout switches. FRIGC™ FR-12™ has poor mineral oil miscibility. FRIGC™ FR-12™ may become weakly or highly flammable due to vapor leakage under cold (about 10 to about 25 degrees Fahrenheit) ambient conditions. However, the amount of flammable mass remaining would be small, in the order of 10 weight percent of the original system charge.    R-22/152a/142b/C318 45/7/5.5/42.5    This is China Sun G2015, or R-405A. R-405A has very marginal mineral oil miscibility, all components are totally immiscible with mineral oil except for R-142b and R-22, which are poor. The R-C318 component is expensive and the R405A mixture was banned (listed as SNAP unacceptable) by the US EPA due to global warming concerns of the R-C318 component, which does not easily break down in the atmosphere, even after several thousand years.    R-22/218/142b 70/5/25    This is R-412A. Although intended as a “drop-in” substitute for R-500, it still has a temperature-pressure curve which is too high for most uses and limited mineral oil miscibility, but slightly better miscibility than Forane® FX-56 and Forane® FX-57 due to more R-142b component. R-218 component is a perfluorinated fluorocarbon with a high global warming potential and a very long atmospheric lifetime, and like R-C318, the US EPA is not approving these compounds for refrigerants.    R-290/600a 60/40    Excellent refrigerant, with excellent oil miscibility. Low cost of components. The problem is the extreme flammability of all components (all hydrocarbons). Blends similar to this have been around a number of years. OZ-12, HC-12a, and ES-12r are tradenames of some similar hydrocarbon blends. At least 14 states have banned the use of hydrocarbon blends for motor vehicle air conditioning along with a Federal ban by the US EPA, which took effect on Jul. 14, 1995.    R-22B1 100    This is Bromodifluoromethane, or Great Lakes Chemical FM-100. The temperature-pressure curve is too low. R-22B1 boils at 4.2 degrees Fahrenheit (R-12 boils at −21.6 degrees Fahrenheit). R-22B1 conta a bromine atom, causing a significant ozone depletion potential, therefore the EPA will not approve its use for refrigerant. R-22B1 has excellent mineral oil miscibility.    R-134a 100    R-134a has complete immiscibility in mineral oil, making it not suitable for most R-12 applications. However, some systems, such as some household refrigerators, may successfully operate using R-134a in mineral oil if the pipe sizes are small enough to generate high enough gas velocities to drag the mineral oil around the refrigeration circuit The compressor is usually located downhill from the evaporator, further minimizing oil return problems with an immiscible oil/refrigerant mixture.    R-152a/22B1 77/23    Good miscibility with mineral oil, but the temperature-pressure curve is too low. Both components have boiling points well above teat of R-12. This mixture may be flammable if vapor leaked at temperatures below about 0 degrees Fahrenheit R-22B1 is not approved by the US EPA for refrigerant use due to high ozone depletion potential.    R-227ea 100    No miscibility with mineral oil and the temperature-pressure curve is much too low.    R-152a/227ea 80/20    No miscibility with mineral oil and the temperature-pressure curve is lower than R-12, causing around a 10 percent reduction in capacity in unmodified systems. This mixture will be flammable, especially when leaking at colder temperatures, below about 0 degrees Fahrenheit.    R-152a/227ea 50/50    No miscibility with mineral oil and the temperature-pressure curve is lower than R-12, causing around a 12 percent to 15 percent reduction in capacity in unmodified systems. This mixture may be flammable, especially when leaking at colder temperatures, below about 0 degrees Fahrenheit.    R-290/227ea 50/50    Good miscibility with mineral oil. Pressure-temperature curve is much too high, almost as high R-22. This mixture will be highly flammable.    R-152a 100    Flammable, but not as bad as propane (R-290). No miscibility with mineral oil. Temperature-pressure curve is too low, causing around a 10 percent reduction in capacity.    R-290/227ea 10/90    Good temperature-pressure curve, and good mineral oil miscibility This blend will be flammable when vapor leaked at temperatures below about 0 degrees Fahrenheit and may be weakly flammable when leaked at higher temperatures. This mixture has a large mass fraction in the higher boiling component (R-227ea), which on some systems may cause unwanted liquid refrigerant return (slugging) to the compressor since there will be a large fraction of the boiling liquid near the exit end of the evaporator. This narrows the margins for charging and suction superheat setup on refrigeration systems.    R-227ea/E170 70/30    R-E170 is dimethyl ether This mixture has good mineral oil miscibility, but the temperature-pressure curve is too low. This mixture may be flammable, especially when vapor leaking at colder temperatures, such as below about 0 degrees Fahrenheit.    R-227ea/600a 75/25    Good mineral oil miscibility, but the temperature-pressure curve is way too low. This mixture might exhibit a region of flammability when vapor leaked in a temperature range of about 0 degrees Fahrenheit, and about 100 degrees Fahrenheit.    R-152a/227ea 20/80    No mineral oil miscibility, and the temperature-pressure curve is too low. This mixture is probably non flammable or possibly weakly flammable over limited regions.    R-152a/13l 25/75    R-13l1 is trifluoroiodomethane (CF3l). Pressure-temperature curve is too low. This mixture has a boiling point of about −8.5 degrees Fahrenheit. There are also concerns of the stability of R-13l1 due to the weakness of the iodine bond. The inventors of this mixture claimed that light broke down R-13l1 and caused refrigerant sight glasses to show purple in about two weeks. The inventors also claimed an extremely high ozone depletion potential for R-13l1, but an almost zero ozone depletion potential after release into the atmosphere after a small number of days (less than a week) due to the breakdown of the CF3l molecule. Toxicity of CF3l is not well established yet.    R-152a/227ea 25/75    No miscibility in mineral oil. The boiling point of −5.2 degrees Fahrenheit indicates a temperature-pressure curve which is too low This mixture may also exhibit regions of flammability when vapor leaked at colder temperatures, below about 10 degrees Fahrenheit.    R-218/134a/600a 9/88/3    This is Isceon 49. Based on a published bubble point of 99 PSIA, the temperature-pressure curve may be a little high, but useable. R-218, a PFC, is now banned by the US EPA for use in refrigerants due to high global warming potential and extremely long atmospheric lifetimes in the thousands of years. Mineral oil miscibility is very poor.    R-22/142b 40/60    Temperature-pressure curve is too low (R-22/142b 55/45 is much closer). Vapor leaking may cause mixture to become weakly flammable, but with no flashpoint. Mineral oil miscibility is poor, but may be useable in high temperature equipment (35 degrees Fahrenheit and higher) for the evaporator temperatures. Mineral oil miscibility is similar to (slightly better than) R-22.    R-134a/600a 80/20    Proposed by Electrolux. Good mineral oil miscibility, but the temperature-pressure curve appears to be slightly high from computer simulations (REFPROP V4.0) and almost azeotropic behavior is exhibited. This mixture appears to have a simulated boiling point about −28 degrees Fahrenheit. It may be a useable substitute for R-500 though. Some azeotropes exhibit a boiling point outside the range (usually lower) of the boiling points of the individual components. The simulated azeotropy point is R-134a/600a 77.83/22.17 for this mixture. An azeotropic mixture behaves, for practical purposes over the temperatures of interest, as a single component refrigerant fluid. During the boiling of the liquid phase of the mixture, all components evaporate at equal rates and fractionation does not occur. The glide is essentially zero. The simulated critical temperature is 211.0 degrees Fahrenheit, which is lower than that of R-134a, which will cause high head pressures in hot environments. This mixture will be flammable.    R-134a/152a 85/15    Boiling points of both components are lower than R-12. Temperature-pressure curve will he slightly too low at evaporator temperatures, but it closely matches that of R-134a (by computer simulation). Azeotropic behavior is observed from simulation, with boiling point of −15.62 degrees Fahrenheit which is practically the same as R-134a. No miscibility with mineral oil. This mixture should be nonflammable or weakly flammable at worst at temperatures of interest, but may be flammable under new strict US flammability standards such as Underwriters Laboratones (UL) 2182 where testing is currently performed at 100 degrees Centigrade.    R-134a/600a 95/5    Mediocre miscibility in mineral oils. The temperature-pressure curve is good (near azeotrope). This mixture should work fine in systems where the compressor does very little “oil pumping” (circulating oil in the refrigerant circuit), such as some household refrigerators. Other systems, especially automotive air conditioner compressors and commercial systems can circulate as much as 10 or 15 percent by volume of oil with the refrigerant. This mixture will not be able to return all the oil under those conditions R-134a has zero oil miscibility by itself, and the addition of a small percentage of a hydrocarbon such as R-600a will not cause the R-134a itself to carry any oil and all the oil will have to be carried by the hydrocarbon. Flammability constraints limit the amount of the hydrocarbon component to around 5 percent.
Five pounds of the R-134a/600a 95/5 mixture were made up for test purposes. About two pounds were charged into the oil miscibility test stand described in Appendix A. Running the evaporator at about −40 degrees Fahrenheit for about 3 hours, caused severe oil return problems, with oil logging observed, and the crankcase oil level dropping. The evaporator temperature was raised to about 5 degrees Fahrenheit by partially closing the manual evaporator pressure regulator valve, and oil continued to become trapped in the evaporator with further observed drooping of the crankcase oil level to near the bottom of the sight glass (compressor running, oil level at top of sight glass at start of run) No oil return was observed at either temperature in the overhead suction line sight glass.
The evaporator temperature was then raised to about 30 degrees Fahrenheit, by the application of about 2500 watts of electrical power to the evaporator. A limited amount of oil was now observed returning to the compressor, as small (amount 1 mm in size) entrained “balls” in the suction gas flow. It was not creeping along the walls of the suction pipes as is usually the case with a mineral oil miscible refrigerant. It can therefore be concluded, that the addition of about 5 percent weight of isobutane to R-134a, provides only very limited mineral oil return capability, for high temperature systems, and is essentially useless for returning oil at lower temperatures of operation. The oil used was Suniso 3GS (150 viscosity).
Since automotive compressor oil has a much higher viscosity than do most oils used for stationary refrigeration (automotive is usually 525 viscosity), the increase in oil return, due to the addition of the isobutane for automotive air conditioning, is expected to be almost nil.
The R-134a/600a 95/5 mixture should be nonflammable at normal temperatures of operation, but may be flammable under new strict US flammability standards such as Underwriters Labs (UL) 2182 where testing is currently performed at 100 degrees Centigrade.    R-218/152a 83.5/16.5    Claims to replace R-12, R-502, and R-22. This composition calculates (with REFPROP V4.0) computer simulation to have a temperature-pressure curve much too high for R-12 replacement. It is closer to R-22. Even if the R-218 weight percentage were drastically reduced and the R-152a increased to achieve a good temperature-pressure curve for R-12, this mixture would still have no mineral oil miscibility. The R-218 is currently banned for refrigerants by the US EPA due to high global warming potential and long atmospheric lifetime.    R-22/142b/600a 55/41/4    This is R-406A, and it has performed satisfactory in the field as a “drop-in” substitute for R-12, and it is nonflammable (after fractionating from vapor leaking) when used by those skilled in the art of refrigeration at normal temperatures of operation of R-12 refrigeration and air conditioning systems Safety testing by several independent labs has verified this. However, new very strict flammability regulations are coming into place in the Unites States, while other countries (many in Europe) are changing over to highly flammable hydrocarbon mixtures of refrigerants. Many refrigerant fluids will be essentially nonflammable at normal temperatures of operation, but may fail a flammability test that specifies an artificially high temperature of operation such as 212 degrees Fahrenheit or higher. R-406A falls into this category.
It is clear from the foregoing discussion that a “drop-in” substitute for R-12, which does not require oil changes and has a higher critical temperature than R-134a, would result in many benefits.
The automotive air conditioning market for a R-12 substitute in the U.S. is huge with an estimated 125 million cars presently left using R-12. It is imperative that “drop-in” R-12 substitutes continue to be developed and used to prevent the costly and premature replacement of billions of dollars worth of refrigeration and air conditioning equipment